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 Method and code for determining selected gear ratio of manual transmissionUSPTO Application #: 20070289400Title: Method and code for determining selected gear ratio of manual transmission Abstract: A method and associated computer-executable code for controlling an automotive powertrain featuring a manual transmission determines a current transmission output speed based at least in part on the vehicle speed achieved in response to a torque request signal; determines an effective transmission gear ratio based on the engine speed and the transmission output speed; and compares the effective transmission gear ratio to each of the predetermined transmission gear ratios. A transmission shift is deemed to be in progress when the effective transmission gear ratio is not within a predetermined tolerance of any of the predetermined transmission gear ratios. Relatively-aggressive smoothing of the torque request signal upon pedal tip-out is advantageously canceled when a shift is deemed to be in progress, thereby reducing the likelihood of unintended engine speed and/or transient flares when a declutching event follows shortly after the pedal tip-out. (end of abstract) Agent: Daimlerchrysler Intellectual Capital Corporation Cims 483-02-19 - Auburn Hills, MI, US Inventors: John S. Mitchell, Amit K. Sanyal, James L. Dowbenko, Ezio N. Vermiglio USPTO Applicaton #: 20070289400 - Class: 74335 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20070289400. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001]The invention relates generally to a method and related computer-executable code for determining which gear of a manual automotive transmission. If any, has been selected by a vehicle operator and, correlatively, for determining when a transmission gear shift is in progress. BACKGROUND OF THE INVENTION [0002]Electronic throttle control (ETC) systems are increasingly being utilized to control airflow into automotive engines to achieve improved vehicle emissions control, vehicle fuel efficiency, and vehicle drivability. In one such system, an engine torque request signal is generated based on a driver demand signal derived, for example, from the output of an accelerator pedal position sensor, perhaps in combination with a number of additional detected or inferred powertrain and/or vehicle operating parameters, and detected or inferred ambient conditions (such as intake air temperature and ambient humidity). A throttle plate in the engine's air intake, as well as perhaps a variation in the engine's nominal intake valve timing, are then controlled in response to the resulting torque request signal to thereby control airflow into the engine and the resulting generated torque output. [0003]In order to improve vehicle drivability and reduce vehicle NVH, known ETC systems advantageously filter or "smooth" the generated torque request signal during demand signal transitions, particularly when the driver "lets up" on the accelerator pedal to thereby rapidly reduce the driver demand signal as sensed by a pedal position sensor (PPS) to a minimum value (also known as throttle "tip-out" and "close pedal"), to obtain a filtered requested torque signal that drops more slowly and ultimately blends into a corresponding minimum torque request. While such requested torque filtering can be particularly advantageous when the engine is coupled to a manual transmission, for example, to avoid generating undesirable drivetrain "clunk" due to mechanical lash within the drivetrain in response to abrupt requested torque transitions, this filtering technique can cause an unintended (upward) engine speed flare if the manual transmission is also being declutched during this filtered requested torque transition. SUMMARY OF THE INVENTION [0004]In accordance with an aspect of the invention, a method and associated computer-executable code are provided for controlling an automotive powertrain to achieve a vehicle speed in response to a driver demand signal, wherein the powertrain includes an engine driving an output shaft at an engine speed, the output shaft being selectively coupled and decouped to a driven wheel through a "manual" transmission having a plurality of manually-selectable gearsets, and a differential having a pinion factor. The method generally includes generating a torque request signal based on the driver demand signal; determining a current transmission output speed based at least in part on the vehicle speed achieved in response to the torque request signal; determining an effective transmission gear ratio based on the engine speed and the transmission output speed; and comparing the effective transmission gear ratio to each of the predetermined transmission gear ratios. [0005]In accordance with an aspect of the invention, the method further includes determining that a transmission shift is in progress, i.e., that a given gearset of the transmission is not fully engaged to thereby couple the engine output shaft to the differential, when the effective transmission gear ratio is not within a predetermined tolerance of any of the predetermined transmission gear ratios. While the invention contemplates use of any suitable tolerances, including different tolerances above and below each of the predetermined transmission gear ratios, in a preferred embodiment, a tolerance band of plus-or-minus five percent (.+-.5%) for each of the predetermined transmission gear ratios is conveniently employed to determine whether a full engagement of one of the transmission's gearsets can be inferred from the determined effective transmission gear ratio. [0006]In accordance with another aspect of the invention, in a preferred method for practicing the invention that further includes filtering the torque request signal over time using a filter coefficient to obtain a second torque request signal, the filter coefficient is modified or, perhaps, all filtering of the torque request signal is inhibited, when the transmission shift is in progress. In this manner, the invention advantageously avoids unintended (upward) engine speed flares when a throttle tip-out is accompanied by a declutching (disengagement) of the transmission. [0007]In accordance with another feature of the invention, the preferred method advantageously determines which gearset of the transmission has been engaged by the driver, based on the comparison of the effective transmission gear ratio with the predetermined transmission gear ratios, without directly sensing either the transmission output speed or, indeed, the transmission/shift linkage itself. [0008]In accordance with yet another aspect of the invention, in a preferred method for controlling a powertrain in which a differential having a predetermined pinion factor (or, alternatively, an activated reducing-gear transfer case and a differential, with a predetermined effective pinion factor) couples the transmission to the driven wheel, the method further includes updating a stored value for the pinion factor (or the effective pinion factor) based on the engine speed and vehicle speed when the method has otherwise determined that the engine output shaft is coupled to the differential by a specific gearset of the transmission, most preferably, by the top-gear-ratio gearset of the transmission shift is in progress. In this manner, the invention advantageously avoids unintended (upward) engine speed flares when a throttle tip-out is accompanied by a declutching (disengagement) of the transmission. [0009]In accordance with another feature of the invention, the resulting transmission shift-in progress information may also be used to determine whether the driver has placed the transmission in neutral. By way of example, a preferred method for practicing the invention further includes determining that the transmission is in neutral if it has been determined that a transmission shift has been "in progress" for at least a minimum time period. While the determination that the transmission has been placed in neutral may be used for any suitable purpose, the preferred method further includes adjusting a minimum value for the torque request signal, preferably by reducing the minimum value for the torque request signal, when it is determined that the transmission is in neutral. In this way, the invention advantageously reduces the potential for drivetrain "clunk" upon reengagement of one of the transmission's gearsets, by increasing the likelihood that engine speed will appropriately be reduced prior to engagement of the gearset. [0010]In accordance with yet another aspect of the invention, the preferred method advantageously determines which gearset of the transmission gear ratio with the predetermined transmission gear ratios, without directly sensing either the transmission output speed or, indeed, the transmission/shift linkage itself. [0011]In accordance with yet another aspect of the invention, in a preferred method for controlling a powertrain in which a differential having a predetermined pinion factor (or, alternatively, an activated reducing-gear transfer case and a differential, with a predetermined effective pinion factor) couples the transmission to the driven wheel, the method further includes updating a stored value for the pinion factor (or the effective pinion factor) based on the engine speed and vehicle speed when the method has otherwise determined that the engine output shaft is coupled to the differential by a specific gearset of the transmission, most preferably, by the top-gear-ratio gearset of the transmission. In this way, the preferred method takes advantage of the learned top-gear ratio of the engine speed to vehicle speed to thereby required only one unique calibration per transmission, and to thereby obviate the need for any axle-specific calibration. And, by using the effective transmission gear ratio to determine whether a transmission shift is in progress, the method of the invention can advantageously be employed in a vehicle powertrain that includes a transfer case, simply by determining the effective pinion factor that is achieved when the transfer was is switched in "low" gear. [0012]Other objects, features, and advantages of the present invention will be readily appreciated upon a review of the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying Drawings. BRIEF DESCRIPTION OF THE DRAWINGS [0013]FIG. 1 is diagrammatic view of an exemplary vehicle powertrain including an electronic control module for controlling the operation of the engine in response to a driver demand signal, in accordance with the invention; [0014]FIG. 2 is a flow chart illustrating the main steps of an exemplary method for determining when the manual transmission of a vehicle powertrain is placed "in gear" by the vehicle's driver and, further, when a transmission shift is otherwise deemed to be "in progress," in accordance with aspects of the invention; [0015]FIGS. 3A-3E are a first set of correlated plots of engine speed, vehicle speed, and the product of vehicle speed, the nominal gearset gear ratio, and the pinion factor; of the determined transmission shift-in progress flag; of the determined effective transmission gear ratio; of the detected driver demand signal, as represented by the output of a pedal position sensor; and of the unfiltered and filtered requested torque signals, all versus time; [0016]FIG. 3F is an enlarged view within Circle 3F of FIG. 3E, again showing unfiltered and filtered requested torque signals versus time; and [0017]FIGS. 4A-4D are a second set of correlated plots of the determined effective gear ratio and the tolerance band associated with the fourth gear ratio, the determined transmission shift-in progress flag, the driver demand signal, and the unfiltered and filtered requested torque signals, all versus time, during a single manual declutching event after the manual transmission has been operating in fourth gear. DETAILED DESCRIPTION OF THE INVENTION [0018]Referring to the Drawings, FIG. 1 is a diagrammatic view of an exemplary powertrain 10 for a motor vehicle that includes an electronic control module ("controller 12") for controlling the operation of an engine 14 based at least in part on a driver demand signal generated by an accelerator pedal position sensor 16, and a manual transmission 18 including several available gears by which the driver selectively couples the engine's output shaft to a driven vehicle wheel 20, either directly through a vehicle differential 22 coupling the transmission's output shaft 24 to the driven wheel's half-shaft 26 or, as seen in FIG. 1, indirectly through a driver-selectable reducing gearset of a transfer case 28. A suitable engine speed sensor 30 and at least on wheel speed sensor 32 generate respective signals from which the controller determines values N, V representative of the current engine speed and current vehicle speed, respectively. [0019]FIG. 2 illustrates the main steps of an exemplary method 34, for use with a vehicle powertrain having a manual transmission such as the one illustrated diagrammatically in FIG. 1, to determine both when the driver has initiated a transmission gear shift (also referred to herein a "shift in progress"), and when the transmission 18 has either been shifted by the driver into a selected one of the transmission's several available gearsets, or has been placed "in neutral." Continue reading... Full patent description for Method and code for determining selected gear ratio of manual transmission Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method and code for determining selected gear ratio of manual transmission patent application. 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